Destruction for unwanted tissue by deep laser heating of water

ABSTRACT

A process for destroying relatively deep formations of unwanted sub-epidermal tissue by heating water in the formations with a laser to denature proteins therein. In an exemplary embodiment, a laser beam is operated to irradiate a target region of highly vascularized dermal tissue in a blood-circulating living being, such as a human. The laser light preferably has a wavelength of about 1.45-1.68  mu m. This operating parameter provides the laser beam with a low enough water absorption coefficient to facilitate adequate penetration in to the target area while still providing enough energy to heat water to a temperature capable of spatially conforming vascularized tissue in the target area.

This application is a file wrapper continuation of application Ser. No.08/564,658, filed Nov. 29, 1995, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the use of lasers to remove unwantedsub-surface tissue from a living being, such as a human. Moreparticularly, the invention concerns a method for selectively destroyingrelatively deep sub-epidermal formations of unwanted tissue by heatingwater in the formations with a laser. This causes protein denaturingsuch as spatial protein conformation, without excessively damaging theunwanted tissue.

2. Description of the Related Art

In the field of cosmetic surgery, one important concern is the treatmentof highly vascularized tissues, such as capillary blood vessels,strawberry hemangiomas, spider veins, telangiectasia, and the like. Inthis respect, many known techniques are aimed at eliminating or reducingsuch tissue. Some of these techniques, for example, include surgicaldissection, sclerotherapy, and electro-cuttering. With surgicaldissection, the patient is first anesthetized and then a cutting devicesuch as a scalpel is used to surgically remove the vascularized tissue.With sclerotherapy, an alcohol-based substance is injected into veinsfor clotting of the veins. With electro-cuttering, a high-voltagescalpel is used to effectively "cut out" the unwanted tissue whilecoagulating blood in the region. Usually, healing of the treated tissueoccurs after formation of a lesion on the skin's surface at thetreatment site.

Although these techniques may be satisfactory in some applications, theymay prove inadequate in certain other circumstances. For instance,certain patients may object to the pain caused by these procedures.Additionally, some patients may experience excessive bleeding,internally and/or externally. Furthermore, these procedures may inflamethe treated tissue in some cases, and lead to healing by second tension.Another potential drawback of known methods concerns the post-treatmenthealing time, which some may find excessive. Further, in certain casesthese techniques have been known to leave scars or other noticeablemarks. Although sclerotherapy may be effective for treating big veins,some may complain that sclerotherapy is not sufficiently effective forsmaller vessels such as capillary blood vessels.

In contrast to the techniques described above, some physicians haveemployed lasers to remove vascularized tissue. In particular, Dye lasershave been used to remove such tissue by destroying blood vessels. Inparticular, the Dye laser process works by exploding red blood cells andconsequently erupting blood vessels. The Dye laser produces wavelengthsthat have little water absorption and therefore generates relativelydeep tissue penetration. On the other hand, the Dye laser produceswavelengths that have a substantial level of oxyhemoglobin absorption.As a result, the Dye laser causes hemoglobin in the erythrocytes to beexploded, causing blood vessel eruption. For some patients, this processmay not be satisfactory. In particular, with small formations such asspider veins and telangiectasia, this approach typically provides only ashort term cosmetic correction of the tissue. Moreover, even afterextended periods of convalescence, many of these patients stillexperience significant scarring.

In contrast to the Dye laser approach, some physicians have usedinfrared lasers at 1.9 μm and greater, such as Tm:YAG, Ho:YAG, Er:YSGG,Er:YAG, CO, and CO₂. These techniques often do not enjoy optimum resultsbecause of certain operating characteristics of the lasers. Chiefly, thelaser is absorbed too readily by water in the patient's tissue,resulting in very poor penetration (e.g., 40-60 μm) of the laser intothe patient's tissue. As a result, significant damage occurs to skinsurface overlying the tissue region of interest. A need therefore existsfor a more effective, less destructive, long term method of destroyingunwanted vascular tissue.

SUMMARY OF THE INVENTION

Broadly, the present invention concerns a process for destroyingrelatively deep sub-epidermal formations of unwanted tissue by heatingwater in the formations with a laser to achieve spatial tissueconformation while avoiding excessive damage to the unwanted tissue. Inan exemplary embodiment, a laser beam is produced to irradiate a targetregion of highly vascularized dermal tissue in a human or other livingbeing with a blood circulatory system. The laser light preferably has awavelength of about 1.45 μm-1.68 μm. This operating parameter providesthe laser beam with a water absorption coefficient that is low enough topenetrate sufficiently into the target area; still, the water absorptionand laser energy are high enough to achieve spatial conformation ofvascularized tissue in the target area. To completely eliminate theunwanted tissue, the laser beam is systematically traced over the entireregion. In accordance with the invention, the destroyed tissue may beeliminated by forceps, vaporized by the laser, or rejected as a necrotictissue by the wound healing process.

The invention affords its users with a number of distinct advantages.Chiefly, the invention effectively destroys sub-surface regions ofvascular tissue, without appreciable damage to the attached orsurrounding tissue. As a result, patients experience little or nobleeding, inflammation, and pain during and after surgery. The inventionalso reduces post-operative healing time and scarring.

BRIEF DESCRIPTION OF THE DRAWINGS

The nature, objects, and advantages of the invention will become moreapparent to those skilled in the art after considering the followingdetailed description in connection with the accompanying drawings, inwhich like reference numerals designate like parts throughout, wherein:

FIG. 1 is a flowchart showing a sequence of process steps in accordancewith the invention;

FIG. 2 is a diagram depicting the irradiation of a target region oftissue;

FIG. 3 is a cross-sectional view of the target region of tissue;

FIG. 4 is a cross-sectional view of the target region of tissue beingirradiated by a laser beam; and

FIG. 5 is a cross-sectional view of the target region of tissue afterirradiation by the laser beam.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Broadly, the present invention concerns a process for destroyingrelatively deep formations of highly vascularized sub-surface tissue ina living being, such as a human or other organism with a bloodcirculatory system. The invention operates by heating water in dermaltissue formations with a laser to achieve spatial tissue proteinconformation therein, while avoiding excessive damage to the region andthe surrounding tissue. This is accomplished by using a laser withoperating characteristics that are selected to achieve appropriatelevels of water absorption, melanin absorption, and tissue penetration,to denature proteins in the unwanted tissue without excessively damagingthat tissue or the surrounding, tissue.

LASER CHARACTERISTICS

Objectionable vascular tissue is typically located beneath theepidermis, about 0.5-2 mm beneath the skin's surface. Vascular tissueburied more deeply is not usually visible through the epidermis. Theblood vessels of the vascular tissue typically include about 55% bloodserum, 44% red blood cells (70% of which comprises water), and 1% whiteblood cells.

With these characteristics in mind, a number of different wavelengths oflaser light were considered to identify a wavelength that provides asuitably low water absorption and complementarily effective penetration.The results appear below in Table 1.

                  TABLE 1                                                         ______________________________________                                                                  AVERAGE  AVERAGE                                                    WAVE-     WATER    MELANIN                                    ENTRY           LENGTH    ABSORPTION                                                                             ABSORPTION                                 NO.    LASER    (μm)   (cm.sup.-1)                                                                            (cm.sup.-1)                                ______________________________________                                        1      Tm:YAG   2.01      ˜100                                                                             <1                                         2      Ho:YAG   2.10      ˜80                                                                              <1                                         3      Er:YSGG  2.78      ˜700                                                                             <1                                         4      Er:YAG   2.94      ˜1000                                                                            <1                                         5      CO       5-6       300-3000 <1                                         6      CO.sub.2 10.6      ˜1500                                                                            <1                                         7      Er:Glass 1.54      1        <1                                         8      Dye      0.55-0.65 <10.sup.-2                                                                             15-10                                      ______________________________________                                    

For the purpose of irradiating a target region located beneath theepidermis, the Er:Glass laser (entry no. 7) provides the best results.Specifically the Er:Glass laser has a low water and melanin absorptioncoefficient that facilitates penetration to the desired depth. Incontrast, entry nos. 1-6 (i.e., those with wavelengths greater than orequal to about 2 μm) have absorption that is dominated by water in thetissue. This results in extremely shallow depth penetration, failing toextend past the epidermis. The Dye laser (entry no. 8) and other laserswith wavelengths less than or about 1 μm have a relatively lower overallabsorption, which is dominated by skin melanin (tissue pigment). Thislower water absorption coefficient results in deeper penetration withvery little water absorption, but a significant amount of absorption intissue melanin. The Er:Glass laser, operating at 1.54 μ, combines thebest features of both wavelength regimes, i.e. deeper penetration due tomoderate absorption in both water and tissue melanin.

Another benefit of the Er:Glass laser is its compatibility with fiberoptics, the usefulness of which is explained below. In particular, theEr:Glass laser produces an appropriate level of power to permittransmission through known fiber optic media.

In the preferred embodiment of the invention, a free-running Er:Glasslaser is employed having operating parameters appropriate to the type ofunwanted tissue being treated, as shown in Table 2 (below). In allcases, the laser is operated with sufficient power to achieve completespatial protein conformation of tissue irradiated by the laser in thelaser's range of penetration.

                  TABLE 2                                                         ______________________________________                                                   PULSE    PULSE-  PULSE    SPOT SIZE                                           ENERGY   WIDTH   REPETITION                                                                             DIAMETER                                 PATHOLOGY  (J)      (ms)    RATE (Hz)                                                                              (nm)                                     ______________________________________                                        SPIDER VEIN                                                                              0.8-1.6  2       0.5      0.6                                      STRAWBERRY 3-4      2       1        0.6                                      HEMANGIOMA                                                                    TELAN-     0.25     2       1        0.6                                      GIECTASIA                                                                     KERATOSIS  2.3-4.3  2       1        0.6                                      CONDYLOMA  4.5-4.7  2       1        0.6                                      SKIN FIBROMA                                                                             3.6-4.0  2       1        0.6                                      BASELIOMA  4.0-4.2  2       1        0.6                                      PIGMENTED  3.5-3.8  2       1        0.6                                      NEVUS                                                                         RHINOPHYMA 1.8-2.5  2       1        0.6                                      LEUKOPLAKIA                                                                              2.5-3.0  2       1        0.6                                      SQUAMOUS   4.2-4.7  2       1        0.6                                      ADENO-                                                                        CARCINOMA                                                                     INTRAMUCAL 4.54.7   2       1        0.6                                      MYOMA                                                                         RECALCITRANT                                                                             3.1-3.5  2       1        0.6                                      VERRUCAE                                                                      CORN       4.0-4.2  2       1        0.6                                      CALLUS     2.7-3.5  2       1        0.6                                      ______________________________________                                    

OPERATIVE STEPS

FIG. 1 provides an example of the present invention in the form ofprocess steps, 100, which are further explained with reference to FIGS.2-5. The steps 100 are performed upon a patient 200 (FIG. 2) by anoperator (not shown), such as a physician, nurse, or physician'sassistant. After the process begins in task 102, the operator in task104 identifies the boundaries of a "target region" 202 of unwantedtissue.

The target region 202 comprises a region of highly vascularizedsub-surface tissue, such as an area of capillary blood vessels,strawberry hemangiomas, spider veins, telangiectasia, or another similarvascular formation. In the illustrated example, the target region 202comprises a sub-epidermal region of capillary blood vessels 300-302,shown most clearly in FIG. 3. FIG. 3 depicts a cross-section of thecapillary blood vessels 300-302 in relation to the dermis 304 andepidermis 306.

After identifying the target region in task 104, the operator in task106 cleans the area of skin 308 overlying the target region. Then, intask 108, the operator irradiates the target region 202 with a laserbeam (not shown) generated by a laser light source 204. Preferably, thelaser beam comprises a beam of laser light generated by an Er:Glasslaser with operating parameters established as shown above.

In one embodiment (FIGS. 2, 4), the laser beam may be carried to thetarget region 202 by a fiber optic waveguide 206, coupled to the lasersource 204. The waveguide 206 may comprise a flexible quartz member, forexample, or another waveguide of suitable flexibility, optical clarity,etc. In this embodiment, the operator contracts a tip (not shown) of thefiber optic waveguide 206 with the target region 202. Alternatively (notshown), the laser beam may be directly impinged upon the target region202. As shown in FIG. 4, when the laser beam enters the skin, it isdiffused, thereby creating a broadened beam 400.

When the laser beam contacts the skin 308 as shown in FIG. 4, the beampenetrates the skin 308 and passes into the target region 202. Thislevel of penetration is possible due to the laser's moderate waterabsorption coefficient, which enables a desirable level of tissuepenetration but prevents an excessive level of tissue penetration. Inthis respect, the laser's water absorption is sufficiently high to heatwater present in the blood capillaries of the target region. Thiseffectively denatures protein molecules in the target region, causing aspatial conformation of the unwanted tissue. In other words, the laserlight is absorbed by the target region 202 causing a moleculartransformation in the form of a local tissue necrosis within a zone oftissue coagulation. The laser beam therefore creates denatured regions500-502 (FIG. 5).

During task 108, the operator must permit the laser beam to contact eachportion of the target region 202 for a sufficient length of time.Namely, irradiation must be continued for enough time to heat the waterin the vascular tissue sufficiently to result in spatial transformationof the tissue. Unlike prior techniques, however, if irradiation in onearea is continued past the time of spatial conformation, the presentinvention does not cause burning, singeing, or other overheating. Thisis because the unwanted tissue, having undergone spatial conformation,is no longer receptive to further transformation by the laser. As aresult, the irradiation of task 108 provides a safe yet effectivetechnique for treating the target region 202.

After the target region 202 is irradiated as discussed above in task108, the operator visually inspects the target region in query 110 todetermine whether the irradiation is complete. If the initial traversalof the target region 202 has inadvertently missed some areas, or failedto sufficiently denature some areas, the operator returns to task 108for additional treatment of the missed areas with the laser beam. Afterprocess is complete, however, the operator stops irradiating the targetregion in task 112.

After task 112, follow-up treatment may be performed in task 114, ifneeded. In particular, denatured tissue of the target region 202 may beremoved and then further irradiation of the target region 202 may beperformed. In one embodiment, the denatured region may be removed with ascalpel and forceps soon after the initial laser treatment of task 108.This enables the operator to treat deeper, underlying areas of thetarget region 202 beneath those areas initially treated. In analternative embodiment, the operator may wait until the treated targetregion 202 heals sufficiently to form a hardened layer of dried blood,i.e., a scab. Then, the operator may remove the scab with a forceps andirradiate the target region again.

OTHER EMBODIMENTS

While there have been shown what are presently considered to bepreferred embodiments of the invention, it will be apparent to thoseskilled in the art that various changes and modifications can be madeherein without departing from the scope of the invention as defined bythe appended claims.

For example, many other lasers may be used instead of an Er:Glass laser.For instance, other lasers may be frequency-modified to achieve awavelength within a range of 1.45 μm to 1.68 μm. Particularly, this canbe accomplished using frequency doubling, frequency tripling, of Ramanshifting, or by employing a different rod, a diode laser, or adiode-pumped solid state or Dye laser. Additionally, a Q-switched lasermay be used, instead of a free-running system.

What is claimed is:
 1. A method of treating discolored regions ofvascularized dermal tissue, comprising the steps of:generating a laserbeam having an absorption coefficient of about 1 cm⁻¹ in water;directing the laser beam toward a target region of dermal tissue;irradiating the target region with the laser beam for heating of thewater in the target region to achieve spatial tissue conformationtherein; and discontinuing irradiation of the target region.
 2. A methodof treating a vascularized tissue region of sub-surface dermal flesh,comprising the steps of irradiating a target area of the dermal tissueregion with a laser beam having operating parameters such that the laserbeam has an absorption coefficient of about 1 cm⁻¹ in water, said laserbeam penetrating through the surface and up to about 2 mm beneath thesurface into the target area and heating water in the target region tospatially conform and cause necrosis to vascularized tissue therein. 3.The method of claim 2, further comprising the steps of tracing the laserbeam along a selected path to irradiate a selected portion of the tissueregion.
 4. The method of claim 3, wherein the selected portion comprisesall of the tissue region.
 5. The method of claim 3, wherein the selectedpath comprises a continuous path.
 6. A method of treating unwantedtissue from a blood-circulating living being, comprising the stepsof:aiming a laser beam at a target region of vascularized dermal tissue,the beam having a wavelength of about 1.45 μm to 1.68 μm; continuing toaim the laser beam at the target region a sufficient time to heat waterin the target region adequately to achieve protein denaturing of thetarget region; and terminating interaction between the laser beam andthe target region.
 7. The method of claim 6, further comprisinggenerating the laser beam wherein the laser beam has a wavelength ofabout 1.54,μm.
 8. A method for treating unwanted sub-surface dermaltissue of a living being having a blood circulatory system, comprisingthe steps of:aiming a laser beam through the surface at a target regionof the sub-surface dermal tissue, the beam having a wavelength of about1.45 μm-1.68 μm; continuing to aim the laser beam at the tissue asufficient time to heat water in the sub-surface target region toachieve protein denaturing and tissue necrosis of vascularized tissue inthe target region; and discontinuing aiming of the laser beam at thetarget region of tissue.
 9. A method of treating dermal tissue beneath askin surface in a living being, comprising the steps of:directing alaser beam through the skin surface to irradiate a target region of thedermal tissue, the laser beam having a wavelength of about 1.45 μm to1.68 μm; continuing irradiation of the target region for sufficientheating of water in the target region to denature tissue proteins of thetarget region and cause tissue necrosis in the target region; and endingirradiation of the target region by the laser beam.
 10. The method ofclaim 1, wherein the living being comprises a human being.
 11. Themethod of claim 1, further comprising using an Er:Glass laser togenerate the laser beam.
 12. The method of claim 1, further comprisingfrequency-doubling output of an Er:YAG laser to generate the laser beam.13. The method of claim 1, wherein the directing of the laser beamcomprises directing the laser beam to a strawberry hemangioma.
 14. Themethod of claim 1, wherein the directing of the laser beam comprisesdirecting the laser beam to a spider vein.
 15. The method of claim 1,wherein the directing of the laser beam comprises directing the laserbeam to a telangiectasia.
 16. The method of claim 1, wherein thedirecting of the laser beam comprises directing the laser beam to atumor of vascularized mucous.
 17. The method of claim 1, wherein theirradiating step is performed by coupling a laser light source to thetarget region with an optical waveguide.
 18. The method of claim 1,wherein the directing of the laser beam comprises directing the laserbeam to a target region located a depth of less than about 2 millimetersbeneath the skin surface of the living being.
 19. The method of claim 1,further comprising generating the laser beam wherein the laser beam hasa pulse energy of about 0.25 to 4 Joules.
 20. The method of claim 1,further comprising generating the laser beam wherein the laser beam hasa pulsewidth of about 2 milliseconds.
 21. The method of claim 1, furthercomprising generating the laser beam wherein the laser beam has a pulserepetition rate of about 0.5 to 1 Hertz.
 22. The method of claim 1,further comprising generating the laser beam wherein the laser beam hasa spot size diameter of about 0.6 millimeters.
 23. The method of claim1, further comprising generating the laser beam by Q-switching a laser.24. The method of claim 1, further comprising generating the laser beamusing a free running laser.
 25. The method of claim 1, furthercomprising the steps of:removing at least a part of the denatured tissueto reveal underlying areas not completely denatured; irradiating theunderlying areas with a laser beam having a wavelength of about 1.45 μmto 1.68 μm; continuing irradiation of the underlying area for sufficientheating of water in the underlying area to denature tissue proteinstherein; and ending irradiation of the underlying areas by the laserbeam.
 26. The method of claim 25, wherein the removing step comprisesthe steps of removing a scab formed by healing of the denatured tissueover a period of time.
 27. The method of claim 25, wherein the removingstep comprises the step of surgically extracting at least a part of thedenatured tissue prior to formation of a scab thereover.